Pachycondyla unidentata Mayr 1862

Southern Mexico south through Amazonia. Costa Rica: Atlantic and Pacific slopes, wet and dry forests, sea level to at least 1200m in places.

Identification

Mandible with more than ten teeth; mesosomal dorsum setose; in side view, dorsal outline of mesosoma forms a continuous convexity including mesonotum, metanotum and propodeal dorsum; propodeal groove obsolete or nearly so, and not strongly impressed; a distinct carina runs from the lateral wing of the clypeus near the mandibular insertion to or nearly to the anteromesal quarter of the margin around the eye; propodeal spiracle slit-shaped; acrotergite of second gastral tergum (when exposed) with a distinctly differentiated median stridulatory file with bands of rainbow colors; arolia present; petiolar node as seen from the side with front face rising abruptly to an angular summit at or near the front, from which it descends behind through a broad curve; posterior face of petiolar node densely and finely punctulate, not striate; clypeus with projecting anteromedian tooth; sides of head above and behind compound eyes smooth, microreticulate, differing from dense and fine punctation of face (figure); all coxae clear yellow orange, rest of leg gradually darkening distally (figure); sides of propodeum with a few rugulae posteroventrally to metanotal spiracle, but dorsolateral face of propodeum smooth and shining (figure).

An LACM specimen from Iquitos, Peru, had surface sculpture like unidentata s.s., but the legs were brown. Legs were consistently yellow in all other specimens of unidentata s.s. I examined.

Similar species:

antecurvata: sides of head above and behind eyes densely punctate, similar to sculpture on face (figure); coxae and legs brown (figure); sides of propodeum with more extensive rugulae between metathoracic spiracle and propodeal spiracle, but rugulae not extending very far onto dorsolateral face of propodeum (figure); dorsolateral face of propodeum punctate, not shiny.

rugosula: head sculpture same as unidentata s.s.(figure); front coxae dark brown with variable stripe of orange at femoral insertion, middle and hind coxae and rest of legs clear orange (figure); sides of propodeum with extensive rugulae between metathoracic spiracle and propodeal spiracle, rugulae extend up over much of dorsolateral face of propodeum (figure).

Natural History

This species is a very common ant in most Costa Rican forests, occurring in the canopy and low arboreal stratum. It is an opportunistic cavity nester, most often using dead branches and stems. It may occasionally be found in Cecropia saplings, and the abandoned carton nests of other ant species. Nests are small, often containing fewer than 10 workers. I once collected two dealate queens together in a small rotten stick, suggesting that pleometrotic founding may occur. The larvae are subject to predation by syrphid flies. The following two accounts are of syrphids found in unidentata nests:

Corcovado National Park, Sirena; 22 December 1981. Dana Meyer found a colony in a piece of rotten stick, hanging vertically at 1m height, outside dia. 9mm, inside 6mm. There were 12 ants total in the nest, including the single queen, 8 pupae, and 8 large larvae. Some may have been lost when the nest was first broken open. Two of the pupae were parasitized. There were fly puparia inside cocoons that had been neatly cut to allow for the greater width of the puparia, making a chinese lantern effect. The cuticle of the puparium was translucent, the organs visible inside. There was a produced, oval callosity on the side with a longitudinal slit in the center of the callosity. A darkly pigmented nipple was on one end. Two parasitoids were isolated from the ants. On 8 January one fly eclosed. Its wings did not expand properly. The puparium opened circumcissally just above the callosity on the ventral side. I put the remaining puparium back in with the ant colony, and the ants immediately picked it up and carried it back into the nest, where they placed it with the rest of the cocoons. They then returned and picked up the naked, empty puparium of the first fly (with much difficulty). They licked and fondled the empty skin for much longer than they licked the first, entire puparium. Finally they put the empty puparium with the cocoons. On 10 January I found the second fly dead outside the ant nest. Its wings had been clipped off, by the ants I presume.

Near Monteverde, 28 July 1984. Nesting in center of suspended rotten stick. The nest contained 4 or 5 parasitized pupae. The cocoons were split down the sides to accomodate the globose fly puparia, creating a chinese lantern effect. I kept four pupae alive in the lab, attempting to rear adults. I removed the surrounding ant cocoon from one of the pupae, and left the cocoons on the remaining three. An adult fly emerged from the naked pupa several days later, but its wings never unfolded properly. I waited another four days, and then observed that the remaining three were dead. They were pharate adults, and the pupal skins had split, but they were trapped inside by the ant cocoons. Thus, the flies must require the presence of the adult ants to remove the cocoon.

Overall, a picture that is emerging is one in which local communities may contain three similar species: (1) unidentata, that prefers open areas and is an opportunistic cavity nester; (2) antecurvata, that occurs in mature forest canopy where it probably nests in live stems; and (3) rugulosa, that is also a mature forest specialist and perhaps even more of a live-stem specialist, being found most often in Cecropia saplings. The first one is morphologically uniform over its broad geographic range; the other two are widespread but show regional differentiation.